Production of pigments

ABSTRACT

A route for the production of a black pigment comprises making an aqueous solution of iron and manganese salts and reacting it with a base in the presence of a protective colloid to produce a granular precipitate. The colloid is preferably in the base but it may also be in the salt solution.

United States Patent Hardy et al.

[151 3,655,418 [451 Apr. 11, 1972 [541 PRODUCTION OF PIGMENTS lnventors:Clarence James Hardy, Wantage; Edward Sydney Lane, Didcot; Mervyn JohnHannam, East l-lendred, all of England Assignee: United Kingdom AtomicEnergy Authority,

London, England Filed: Aug. 14, 1969 Appl. No.: 850,217

Foreign Application Priority Data Aug. 20, 1968 Great Britain..39,748/68 U.S. Cl. "106/304, 106/308 Q, 106/309 Int. Cl. ..C09c 1/24,C08h 17/04 Field of Search ..106/304, 308 Q, 193 J, 308 P,

Primary Examiner-Tobias E. Levow Assistant Examiner-J. V. HowardAttorney-Larson, Taylor & Hinds [57] ABSTRACT A route for the productionof a black pigment comprises making an aqueous solution of iron andmanganese salts and reacting it with a base in the presence of aprotective colloid to produce a granular precipitate. The colloid ispreferably in the base but it may also be in the salt solution.

10 Claims, N0 Drawings PRODUCTION OF PIGMENTS The present inventionrelates to the production of pigments and more specifically to theproduction of a black or dark grey pigment which is stable at hightemperatures. It has heretofore been proposed to use black pigmentsbased on magnetite but unfortunately these pigments decompose to ferricoxide at temperatures above 180 C. and since ferric oxide is brown incolor this means that the black pigment is not stable. It has also beenproposed to use a mixture of iron oxide and manganese oxide as a blockpigment, the mixture being color stable up to temperatures of the orderof 800 C. but unfortunately the preparation of such pigments hashitherto been complex, a route being described in British Pat. No.1,082,847.

It is an object of the present invention to provide a new or improvedroute for the manufacture of iron-oxide-manganeseoxide pigments.

According to the present invention there is provided a process for theproduction of a pigment, comprising forming an aqueous solutioncontaining water-soluble iron and manganese salts, introducing suchaqueous salt solution into an aqueous solution of a base in the presenceof a protective colloid thereby to form discrete particles, andfiltering, washing and calcining such particles.

More specifically the soluble iron salts which may be used are ferricnitrate, ferric chloride and ferrous sulphate and the soluble manganesesalts are conveniently manganese nitrate or manganese sulphate. Forcheapness it is convenient to generate manganese sulphate by reaction ofmanganese dioxide with sulphuric acid in the presence of an easilyreduced organic reactant, such as formaldehyde. The manganese sulphatedoes not have to be used with ferric sulphate but can be used with thechloride which is also cheap.

A solution is made up containing the iron and manganese salts in therequired proportions and then this solution is dropped into a solutionof a base such as ammonia or sodium hydroxide.

The protective colloid may be present either in the solution of salts orin the base, the latter being preferred. The use of protective colloidsin the salt solution is to some extent disclosed in our copending UK.application No. 15525/66, issued as British Pat. No. 1,175,834.

The protective colloid is a water-soluble organic polymeric compound andmay for example be a polyhydroxy compound such as dextran, a cellulosederivative, polyvinyl alcohol or starch, a polycarboxylic compound suchas Rohafioc L2 (a methacrylate polymer), a polycarbonamide compound suchas Polyflok 4D (an anionic acrylic polymer), a polyamine compound suchas gelatin or a mixture of these compounds.

On dropping the salt solution into the base generally sphericalparticles of gel are formed, this gel being either the hydroxide or thebasic sulphate. After standing in the base for a sufficient length oftime the gel particles are relatively hard and may be filtered withoutdifficulty. The particles may then be washed or even leached to removeunwanted ions, although a considerable percentage of sulphate and/orsodium ions can be tolerated in the final product.

The gel particles are then conveniently dried for several hours at atemperature below 100 C. to remove excess water and allow furtheroxidation. If desired and if based on nitrate solutions, they may bedenitrated at a temperature of about 500 C. They may then be calcined inair at a temperature in the range 750-850 C. to develop a stable blackpigmentf This pigment shows no color change after being heated to 850 C.and re-cooled.

The ratio of iron to manganese by weight is conveniently in the range3:1 to 12:1, the color varying from deep grey to black with increasingmanganese content.

It will be appreciated that the technique described enables filteringand washing to be carried out quickly, easily and effectively incontrast to a conventional co-precipitation route in which formation offinely divided gelatinous precipitates leads to loss of manganese as afilter-passing colloid and blocking of the filters by iron hydroxide.

The product is relatively soft and after calcining can be ground or ballmilled easily to reduce its particle size to the required value.

In order that the present invention may more readily be understood,certain examples of preparations in accordance with the same will now bedescribed.

EXAMPLE 1 500 g. of ferric nitrate (FE(NO;,) ,9H O) and 45 g. ofmanganese nitrate (Mn(NO ,6H O) were dissolved in 1 liter of water. Thissolution was sprayed through a hypodermic needle.

into 2 liters of a solution of 50 percent 0.880 ammonia in watercontaining 40 g. of soluble starch. The ammonia was stirred until thereaction was completed and the precipitate allowed to settle overnight.The precipitate was then retained on a sintered filter plate and washedwith four times its volume of water, before being tray dried for 18hours in a circulating hot air oven at C. The material was heated in airat 500 C. for 1 hour to remove nitrate, and finally calcined at 800 C.for 1 hour to produce a black pigment with an iron to manganese ration(by weight) of 8: l/

EXAMPLE 2 350 g. of ferrous sulphate (FeSO ,7l-l O) and 66 g. ofmanganese sulphate (MnSQ H O) were dissolved in 1 liter of water andadded to a solution of 200 g. of sodium hydroxide and 10 g. of solublestarch dissolved in 1 liter of water and held at 70 C. The gelprecipitate was filtered and washed once with its own volume of water.It was then dried for 24 hours in air at 95 C. on shallow trays to aidoxidation. The product was finally calcined for 2 hours in air at 850 C.The pigment had an iron to manganese ratio (by weight) of 3.3:1 and ananalysis of 41.5"lo iron, 12.7 /o Mn, 11/o SO ,6"/o Na.

EXAMPLE 3 20 g. of manganese dioxide was boiled with 300 ml. of watercontaining 30 ml. of concentrated sulphuric acid. 50 m1. of formaldehydesolution (35 g. per ml.) was slowly added to aid the dissolution of themanganese dioxide. 270.3 g. of ferric chloride hexahydrate dissolved in500 ml. of water was then added. 20 g. of Rohafioc L2 was stirred inuntil the mixture was homogeneous. The mixture was sprayed through anatomiser into 2 liters of 8M ammonia containing 2 percent by volume ofRohafioc L2. The precipitate was treated as described in Example 1 togive a black pigment.

EXAMPLE 4 20 g. of manganese dioxide was boiled with 300 ml. of watercontaining 30 ml. of concentrated sulphuric acid. 50 ml. of formaldehydesolution (35 g. per 100 ml.) was slowly added to aid the dissolution ofthe manganese dioxide. 270.3 g. of ferric chloride hexahydrate dissolvedin 500 ml. of water was then added and the mixture sprayed into 2 litersof 8M ammonia containing 40 g. of soluble starch. The precipitate wastreated as described in Example 1 to give a black pigment.

We claim:

1. A process for the production of a pigment comprising forming anaqueous solution containing water-soluble iron and manganese salts,forming the said aqueous salt solution into a plurality of discreteparticles, gelling the particles by contacting them with an aqueoussolution of a base in the presence of a protective colloid, filteringthe gelled particles, washing the filtered particles and calcining thewashed particles.

2. The process of claim 1, wherein said aqueous salt solution is formedby dissolving manganese dioxide in dilute sulphuric acid and adding aferric salt.

3. The process of claim 1, wherein the protective colloid is present inthe aqueous base solution.

4. The process of claim 1, wherein the protective colloid is selectedfrom the group of water-soluble organic compounds 7. The process ofclaim 1, wherein the precipitate is dried at a temperature below C.

8. The process of claim 1, wherein the precipitate contains nitrate ionsand is denitrated at a temperature of about 500 C.

9. The process of claim 1, wherein the precipitate is calcined in air at7SO-850 C.

10. The process of claim 1, wherein the ratio of iron to manganese is inthe range 3:] to l2: l by weight.

2. The process of claim 1, wherein said aqueous salt solution is formedby dissolving manganese dioxide in dilute sulphuric acid and adding aferric salt.
 3. The process of claim 1, wherein the protective colloidis present in the aqueous base solution.
 4. The process of claim 1,wherein the protective colloid is selected from the group ofwater-soluble organic compounds consisting of polyhydroxy compounds,polycarboxylic compounds, polycarbonamide compounds and polyaminecompounds.
 5. A process according to claim 4, wherein the colloid isselected from the group consisting of dextran, water-soluble cellulosederivatives, polyvinyl alcohol water-soluble starch derivatives,water-soluble methacrylate polymers, and gelatin.
 6. The process ofclaim 1, wherein the precipitate is leached to reduce the proportion ofunwanted ions.
 7. The process of claim 1, wherein the precipitate isdried at a temperature below 100* C.
 8. The process of claim 1, whereinthe precipitate contains nitrate ions and is denitrated at a temperatureof about 500* C.
 9. The process of claim 1, wherein the precipitate iscalcined in air at 750*-850* C.
 10. The process of claim 1, wherein theratio of iron to manganese is in the range 3:1 to 12:1 by weight.